Imitation-leather material and method of preparing such material

ABSTRACT

An imitation-leather sheet laminate material is prepared employing an acidic, heat-coagulated, carboxylated, elastomeric latex polymer, wherein the acidic latex polymer is coated onto a top resin skin layer and a fibrous base sheet is placed on the wet foam layer, which method comprises: shock-heating the wet foam layer to coagulate the carboxylated polymer therein into a fine, open-cell, tough foam layer and to remove rapidly water from the coagulated foam layer.

BACKGROUND OF THE INVENTION

Foamable latex formulations have been employed in the preparation oflaminate sheet materials suitable for use as imitation-leather products;for example, for the production of shoes, handbags, clothing and thelike. One method employed is known as the "wet-gap laminationtechnique", and is described in particular with specific formulationsand techniques in connection with U.S. Pat. No. 4,002,792, issued Jan.11, 1977, hereby incorporated by reference in its entirety. In thistechnique, a polymeric skin layer is formed, such as by casting apolymer solution onto an embossed release sheet, and, thereafter,mechanically foaming a latex and coating a layer of wet foam onto theembossed skin layer. Prior to drying, a base sheet material, such asfibrous sheet material, napped or unnapped, is placed on top of the wetfoam layer. The wet-foam-coated paper at the bottom is then brought intocontact with a base fabric sheet at the top through a pair of rolls orbars with a predetermined nip to form a laminate. Thereafter, thewet-gap laminate material so formed is dried in an oven to remove waterfrom the foam layer and then subsequently is heated in another oven tocross-link or cure the dried latex foam polymer.

In another embodiment, using an adhesive-post-laminate process, the wetfoamable latex layer on the skin layer is first dried, and then anadhesive tie-in layer; for example, 1 to 20 wet mils and less than thefoam layer, is coated onto the top of the dried latex layer. Thereafter,the base sheet material, such as the fabric, is placed on the wetadhesive layer and the laminate sheet material is than heated to cure orcross-link the latex layer. This post-adhesive-laminate process avoidsthe difficulties of evaporating a large amount of water out of the wetfoam layer in the laminate, but involves a separate adhesive-coatingoperation and oven. The laminate formed is often run through a set ofbars or rolls to press down with considerable force the fabric base intothe adhesive layer before heating to cure the foam layer.

In producing such laminate sheet material, care must be taken as regardsthe production speeds employed and the degree of heating at variousstages, in order to avoid blistering of the laminate material by toorapid heating to remove the water and trapping of the moisture vaporwithin the internal portion of the laminate. Thus, the wet-gaplamination technique, while satisfactory in many respects, typicallyrequires limited production speeds in order to avoid rapid heating, andalso requires the capital expense and need for two separate ovensystems: one a drying oven system and the other a curing orcross-linking oven system. The post-adhesive-laminate process involvesthe use of an adhesive and a separate oven and casting process.

Therefore, it is desirable to overcome the disadvantages in the wet-gaplamination system and post-adhesive-laminte process, and to provide newand improved sheet laminte materials.

SUMMARY OF THE INVENTION

Our invention concerns improved latex-foam-coated and laminatematerials, particularly flexible sheet laminate materials, suitable foruse as imitation-leather materials or for use in preparing suchmaterials, and to a method of preparing such coated and laminate sheetmaterials. More particularly, our invention relates to an improvedimitation-leather material containing a latex-foam core layer derivedfrom a foamable polymeric latex, and to the method of preparing suchimproved imitation-leather material.

Our method comprises an improvement over the wet-gap laminationtechnique, wherein the polymeric wet foam layer is a heat-coagulablefoamable latex layer, and wherein the improvement comprises the step ofcoagulating the polymeric material from the wet foam layer afterformation of the foam-coated or laminate sheet material, to provide afoam layer of heat-coagulated polymer characterized by a high densitytypically, but not necessarily, over 40 pounds per cubic foot (pcf); forexample, over 50 pcf, and having a fine-cell structure. The coagulatedfoam layer permits the subsequent and rapid heating of the sheetmaterial and the easy and effective removal of water therefrom, withoutblistering of the product.

Our method permits the preparation of the entire sheet laminate; thatis, with the polymeric skin layer or imitation embossed leather designlayer composed of, for example, vinyl-chloride or urethane-elastomerresin, and of the employment of a base sheet layer, such as a fibrouslayer like a woven or nonwoven fibrous natural or synthetic material,with one or more intervening latex foam layers.

We have found that both the wet-gap lamination process and thepost-adhesive-lamination process are improved considerably by theemployment of a heat-coagulable, foamable latex layer. The employment ofa rapidly coagulable wet foam layer provides for a fine, tough, dense,fast-drying and fast-curing foam layer. Heat-coagulation of the foam inthe wet-gap lamination process provides significant improvement, sincethe rapid heat-shock coagulation of the wet foam layer; for example, attemperatures of 375° F. or less, permits the easy and rapid removal ofthe water from the coagulated foam, without the danger of blisteringwith high oven temperatures or slow production-line speeds. Our processparticularly is useful with the wet-gap lamination process, since theamount of water to be removed, by evaporation through the fabric bassheet, is reduced. Our process also is useful in thepost-adhesive-lamination process, since the rapid and easy removal ofwater from the wet foam layer permits the adhesive tie-in layer to beapplied and dried more quickly. Since the coagulated foam layersemployed, unlike the carpet or mattress field, are relatively thin; forexample, less than about 50 mils dry, the problems of curling associatedwith thick, coagulated, latex foam layers is avoided or minimized.

In our preferred method, a heat-coagulable, foamable latex compositionis employed, wherein a natural or synthetic elastomeric/polymeric foamcomposition is heat-coagulable. The polymeric latex preferably isheat-coagulable by the addition of an acid or acid salt to place thefoam latex at a pH of less than about 5.0, and more particularly at a pHof less than 3.0; for example, 2.0 to 3.0, so that the heat-coagulatingtemperature preferably is about 325° F. to 350° F.; for example, 275° F.to 350° F. The gel points of our coagulable latex foam typically isadjusted to be about 120° F.; for example, 110° F. to 115° F.Shock-heating of the coagulable latex should be at an oven temperatureof less than 450° F. to coagulate the latex and to remove water andeffect polymer cure. The acidic latex formulation does not have a longpot life; for example, often less than 8 hours, but ammonia may be addedto raise the pH and extend the pot life as desired. The foamable latexmay be made heat-sensitive or -coagulable by acids or other additives,or combinations thereof; however, the use of acids, due to cost andsimplicity, is preferred. For example, a sufficient amount ofheat-coagulable materail for the polymer, such as a functionalpolysiloxane or siloxane copolymer, such as copolymers of methylsiloxaneand dimethylsiloxane and hydroxyalkyl polyols, may be used.

The foamable latex formulation is maintained on the acidic side, andparticularly is maintained on the acidic side with the use of an acid oracid salt, such as a strong acid like paratoluene sulfonic acid;however, if desired, other acids like sodium silica fluoride, tartaricacid, oxalic acid and their salts may be used.

Such acidic, heat-coagulable, mechanically foamable latex formulationspermit the coagulation of the polymer from the wet foam latex layer onheating, with the subsequent result that water may be removed easily andquickly from the coagulated latex layer by rapid heating through thesubstantially open-cell fine structure of the coagulated foam layer. Ourmethod avoids the employment of separate drying and curing ovens, andalso permits the very rapid production-line speeds in the production ofsheet laminate materials, since the materail may be heated rapidlywithout danger of blistering, due to the rapid removal of water. Ourmethod permits the elimination or makes optional the use of adhesivetie-coat layers, particularly when the wet foam laminate layer is placedon the napped side of a nap sheet fabric, such as where a fabric is tobe employed as a shoe-upper material. Where an adhesive layer is placedthereon, the adhesive tie-coat layer tends to be wicked up, leaving anadhesive-starved interface. In the wet-gap lamination process, thenapped fibers of the napped side wick up the water from the dense andmuch-higher-gauze wet foam layer and permit even, rapid removal of thewater from the wet foam layer with the use of napped-base fabrics.

Our improved method provides for a coagulation of the elastomeric latexpolymer from a wet foam layer in a controlled manner typically by theemployment of heat and the use of an acidic latex, to provide adifferent type of coagulated foam with a fine substructure of highdensity and a substantially open-cell character, which permit the rapidand easy removal of water, while maintaining the preparation of a veryflexible and desirable imitation-leather material suitable for use, forexample, as shoe uppers.

In our method, the polymer of the foamable latex layer may be coagulatedby a number of techniques. However, our preferred embodiment is tocoagulate the foam by maintaining the foam as strongly acidic by the useof paratoluene sulfonic acid or acid salt or a similarly strong acid,and optionally, if desired, also by employing a heat-sensitizing agentwhich reduces the gel- or heat-coagulation temperature of the foam, suchas a siloxane-type compound.

The sheet laminate material of our invention may comprise a toppolymeric skin layer which may or may not be embossed with a grain orother surface-design pattern thereon, one or more layers ofcoagulated-foam-flexible latex, and a base layer, typically a woven ornonwoven fibrous base sheet, such as a napped cotton fabric. Adhesivetie layers may be employed if desired, but are not necessary. Inaddition, our method permits the preparation of the wet foam layerdirectly on the napped side of a napped base fabric at commerciallyacceptable speeds; for example, over 200 hards per hour.

In an even broader connotation, our coagulated foam layer may be used toprepare a laminate material consisting of a base sheet and a coagulateddried and cured foam layer of various densities thereon; that is, alaminate material without the necessity of a solid skin layer of avinyl-chloride or urethane or other resin. For example, such a sheetmaterial may be prepared by foaming an acidic, heat-coagulable polymericlatex and coating the foamable layer onto an embossed paper-releasesheet; for example, 5 to 100 mils, and then placing a wet-gap laminationbase sheet; for example, a napped fabric, onto the wet foam layer andrapidly heating the wet laminate structure; for example, 275° F. to 375°F., to coagulate the polymer and to remove water, and, thereafter,stripping off the release sheet to provide a dry laminate product havingthe base layer securely and directly adhered to a dry, coagulated, fine,dense foam layer which may have a surface-design effect thereon from theembossed release paper. The coagulated polymer foam layer with the fine,tough, dense cell structure often presents a fine-grain, imitation-likesurface without the need for employing a skin or other top-coatinglayers. Our invention not only avoids the difficulties associated withprior foamable latices employed in preparing imitation-leathermaterials, but also avoids the difficulties associated with the use oforganic-solution urethanes and the coagulation of urethane from organicsolutions; for example, by employing a water bath, which requires suchcoagulated urethanes to be heated subsequently to remove the water ofcoagulation.

A wide variety of polymers may be employed in the foamable polymericlatex compositions employed in our method and material. However, suchpolymers typically should be such as to be stable or relatively stableand on the acid side, and may comprise, but not be limited to, syntheticelastomers of nitrile- or diene-conjugated elastomers or copolymers orterpolymers containing such diene and nitrile compounds. Such elastomersinclude, for example, acrylonitrile-butadiene copolymers andcarboxylated elastomers such as to cure with the use of aminoplastresins, such as melamine-formaldehyde resins. Syitable elastomersinclude acrylonitrile-diene-acrylic terpolymers, such asacrylonitrilebutadiene-acrylic polymers.

Heat-coagulable, foamable latex formulations for use in our methodcomprise an aqueous latex with a synthetic elastomer, optionally theaddition of minor amounts; for example, 5% to 30% by weight, of othercompatible polymers like vinyl-halide resin, such as polyvinyl-chlorideand vinyl-chloride/vinyl-acetate copolymers, to modify the elastomerproperties, such as to provide better hand and suppleness to the foam,surfactants; for example, 0.1% to 5% by weight, to stabilize the foamand permit mechanical frothing, a curing or cross-linking agent; forexample, 0.5% to 20% by weight, viscosity-control agents, fillers, suchas clay, alumina, diatomaceous earth and the like, pigments, dyes,stabilizers, flame retardants, plasticizers, heat-sentisitizing agentsand the like. The amount of the acid or acid salt may vary, depending onthe gel point and pH desired, but often ranges from about 0.5% to 3% byweight. The foamable latex should be mechanically frothed afterpreparation and cast onto the paper or other release sheet, without orwith a thin polymeric skin layer; for example, 0.1 to 5 mils. The coatedsheet or laminate, if a base fabric is used, is introduced into ahot-air or steam oven at 350° F. to 375° F., wherein the heat shockcoagulates the latex foam to drive off the water. After drying the foamis cured by heating; for example, 375° F. to 425° F., in the same orseparate oven. The materials and procedure employed are as described inU.S. Pat. No. 4,002,792, except that the acidic heat-coagulable foam isused.

DESCRIPTION OF THE EMBODIMENTS

A foamable latex formulation was prepared by admixing the followingcomponents:

    ______________________________________                                                                          pHR (parts per                                               Total           hundred parts                                Ingredients      Solids  Wet     of resin)                                    ______________________________________                                        1.  Hycar 1572 X 45, a car-                                                        boxylated acrylonitrile-                                                      butadiene emulsion co-                                                        polymer          47%    96.0  94.8                                       2.  Vinyl-chloride polymer-                                                        modifier         50%    5.0   5.2                                        3.  Curing agent - methyla-                                                        ted melamine-formalde-                                                        hyde resin (Cymel 303,                                                        American Cyanamid Co.)                                                                         85%    4.0   7.1                                        4.  Surfactant - Sodium                                                            lauryl sulfate   3.0%   0.5   0.3                                        5.  Paratoluene sulfonic                                                           acid monohydrate                                                                              100%    8.5   1.7                                        6.  Alumina hydrate flame-                                                         retardant - filler                                                                            100%    8.5   17.8                                       7.  Thickening agent -                                                             methyl cellulose                                                                              100%    0.5   1.1                                        ______________________________________                                    

The latex formulation so prepared had a viscosity of 5,000 to 10,000cps, Brookfield spindle #4 rpm 20, a specific gravity of 1.094 and a pHof 2.0. The gel point of the latex was 110° F. to 120° F. The latex wasmechanically foamed and a wet foam layer of 18 to 30 mils; for example,25 mils (16 mils dry) was coated onto the surface of a thin, elastomericurethane skin layer, 0.3 to 0.8 mils previously cast onto an embossedrelease paper. A napped cotton base fabric, with the napped side down,was placed on the wet foam layer and the wet laminate formed was passedthrough a pair of nip rollers. The laminate was then heated in asteam-heated oven to 350° F. to coagulate the nitrile-diene coagulatedpolymer by shock-heating and to drive off the water from the dense,fine, open-cell foam formed by such shock-heating. Heating is continuedin the same oven to cure the coagulated foam. The laminate recovered hadgood hand, was supple and tough, with a foam layer density of 50 to 60pcf; for example 58 pcf. The same noncoagulable formulation, without theaddition of paratoluene sulfonic acid or with only minor amounts andhaving a slightly acidic pH, for example, of 6.0 to 6.5 in the sameprocess, provided unsatisfactory laminates. The introduction of the wetlaminate into the 350° F. oven resulted in a poor, weak, large-cell,innerfoam-cure composition and illustrated unsatisfactory laminates.

Our invention has been described particularly in its preferredembodiment as an improvement on the wet-gap lamination method. However,it is recognized and is a part of our invention that heat-coagulableelastomeric foams in thin layers may be used as an inner-core foam withleather substitutes, or as the embossed or nonembossed surface layer ona base sheet; that is, where the fine, dense, heat-coagulated foam formsthe leather-substitute surface.

What we claim is:
 1. In a method of preparing an imitation leather sheetmaterial, which method comprises:(a) coating a thin, wet foam layer of afoam latex composition onto a flexible sheet material, the latexcomposition comprising a film-forming, elastomeric, cross-linkable,carboxylated polymer and a cross-linking agent for the carboxylatedpolymer; (b) placing a fibrous base steet material onto the top surfaceof the wet foam latex layer to provide a wet laminate product; and (c)heating the wet laminate product to dry and cure the foam layer and toprovide a dry laminate product, the improvement which comprises:(i)providing a heat-coagulable, polymeric acidic latex composition as thewet foam layer and wherein the latex composition includes an acid or anacid salt to reduce the pH to less than 5.0, and (ii) shock-heating thewet foam layer of the wet laminate product by rapidly heating the wetfoam layer in a single heating oven operation and in a singletemperature step to a temperature of not greater than 450° F. andgreater than about 250° F. to heat-coagulate rapidly the acidic polymerto a fine, dense, open-cell foam structure and to remove water rapidlyfrom the coagulated foam layer without blistering of the foam layer toform a dry foam layer and to cross-link the coagulated dried polymer,all during such single temperature step and in such single oven.
 2. Themethod of claim 1 wherein the polymer has a gel temperature of fromabout 125° F. or less.
 3. The method of claim 1 wherein the latexcomposition has a pH of from about 2.0 to 5.0.
 4. The method of claim 1wherein the latex composition includes a paratoluene sulfonic acid oracid salt to reduce the pH to a pH of from about 2.0 to 3.5.
 5. Themethod of claim 1 wherein the latex composition includes aheat-sensitizing coagulant which comprises a polysiloxane compound. 6.The method of claim 1 wherein the polymer comprises a carboxylated,acrylonitrile-butadiene elastomeric polymer and the curing agent is amethylated amino resin.
 7. The method of claim 1 wherein the latexcomposition includes from about 5% to 30% by weight of the compositionof a vinyl-halide polymer.
 8. The method of claim 1 wherein theheat-coagulated dry foam layer and the dry laminate product has a dryfoam density of greater than about 50 pounds per cubic foot.
 9. Themethod of claim 1 wherein the fibrous base sheet comprises a nap fabricsheet and the nap fabric side of the sheet is placed in contact with thewet foam layer, and wherein the flexible sheet material comprises athin, elastomeric urethane resin or a vinyl-halide resin on a releasepaper, and which method includes the step of stripping the release paperfrom the resin layer to provide an imitation-leather sheet laminatematerial.
 10. The method of claim 1 wherein the dry heat-coagulated foamlayer has a thickness of from about 5 to 50 mils.
 11. The method ofclaim 1 wherein the flexible sheet material comprises a release paper,and which includes the step of stripping the release paper from the dryfoam layer of the dry laminate product to provide an imitation-leathersheet material which comprises the dry heat-coagulated polymer as a drylayer bonded to the fibrous base sheet material.
 12. The method of claim1 wherein the latex composition has a pH of less than 5.0 and includes asmall amount of a paratoluene sulfonic acid, and shock-heating of thewet laminate product is carried out at a temperature of from 275° F. to350° F.
 13. The product produced by the method of claim
 1. 14. Theproduct produced by the method of claim 1 wherein the flexible sheetmaterial is stripped from the dry laminate product to provide animitation-leather sheet material.
 15. In a method of preparing animitation leather laminate sheet material, which method comprises:coating a thin, wet foam layer of from about 5 to 100 mils of a foamedcarboxylated acrylonitrile-butadiene latex composition onto a thin, topskin layer of a urethane resin or vinyl-chloride resin on a releasepaper, the latex composition containing a methylated amino resincross-linking agent for the carboxylated polymer and a foaming agent topermit mechanical frothing of the latex composition, placing a nappedfabric sheet material onto the top surface of the wet foam layer, thenapped surface down and in contact with the wet foam layer to provide awet laminate product, and heating the wet laminate product to dry andcure the foam layer, and, thereafter, removing the release sheet fromthe urethane resin or vinyl-chloride resin layer to provide animitation-leather substitute material, the improvement whichcomprises:(a) providing a heat-coagulable, polymeric,acrylonitrile-butadiene, carboxylated polymer composition which has a pHof less than 5.0 and which contains paratoluene sulfonic acid, toprovide a heat-coagulated polymer having a gel temperature of about 125°F. or less; and (b) shock-heating the wet foam layer of the wet laminateproduct by rapidly heating the wet foam layer in a single heating ovenoperation and in a single temperature step to a temperature of fromabout 275° F. to 350° F. to heat-coagulate rapidly the carboxylatedacrylonitrile-butadiene polymer into a fine, dense, open-cell foamstructure, the foam having a dry density of about 50 pounds per cubicfoot or greater to remove water rapidly from the coagulated foam layerwithout blistering of the foam layer to form a dry foam layer and tocross-link the coagulated dried polymer, all during such singletemperature step and in such single oven.
 16. A method of preparing animitation-leather material, which method comprises:(a) mechanicallyfoaming an acidic, heat-coagulated, elastomeric/polymeric latex having apH of 5.0 or less; (b) coating a thin layer of the foam latex onto anembossed paper-release sheet; (c) placing a fibrous base sheet onto thewet foam layer to provide a wet laminate product; (d) shock-heating thewet laminate product by rapidly heating the wet foam layer in a singleheating oven operation and in a single temperature step toheat-coagulate rapidly the acidic polymer into a dense, fine, tough,opencell foam structure and to remove water rapidly therefrom withoutblistering of the foam layer to form a dry foam layer, the shock-heatingcarried out a temperature of more than 250° F. and not greater than 450°F; and, thereafter, (e) stripping off the paper-release sheet to providea laminate product having a base fibrous layer securely adhered to acoagulated dried polymeric foam layer.
 17. The method of claim 16wherein the paper-release sheet has an embossed design thereon, whereby,on stripping the paper-release sheet from the dry, coagulated foamlayer, the foam layer having an embossed design thereon.
 18. Thelaminate product produced by the method of claim
 16. 19. The laminateproduct produced by the method of claim 15.